The present invention relates to a method and apparatus for the non-invasive diagnosis and therapeutic management of patients having systemic hypertension or other critical illnesses, and, more particularly, to a method and apparatus for determining a therapy to achieve both a normotensive and normodynamic state or a selected stated dictated by conditions to increase the probability of survival after surgery, trauma, illness, or the like.
Hypertension is typically diagnosed through a non-invasive measurement of systolic and diastolic arterial pressure values by a sphygmomanometer, and by comparing the obtained "blood pressure" values to values considered "normal" for that particular patient taking into consideration the sex, age and body habitus. Once diagnosed, hypertension today is predominantly treated by prescription of any of a variety of classes of drugs which are pharmacologically capable of reducing the measured blood pressure value. Hypertension is then considered under control when the measured arterial pressures reach the normal range.
Although the use of such single modality therapy is generally quite successful in achieving the desired variation in the measured blood pressure, it does not take into account the patient's status with regard to more important hemodynamic parameters, such as cardiac output. Hypertensive drugs can be prescribed which have the additional and unmeasured effect of simultaneously lowering cardiac output. Thus, notwithstanding attainment of the normotensive end goal of therapy, important hemodynamic deviations can remain, or even be induced by the prescribed therapy. The resulting diminished perfusion could be reasons for so-called side effects of hypertension therapy, such as dizziness, impotence and general down feeling, which the patient typically did not experience prior to diagnosis and traditional treatment of hypertension. Hence, current hypertension therapy could lead to prolonged duration of the treatment, higher cost to the patient and/or medical insurance carrier, adverse side effects resulting in patient's noncompliance, and general lowering of the patient's quality of life.
The importance of precise differentiation between normotensive therapy and effects on the hemodynamic state have recently been underscored by the work of W. C. Shoemaker, M.D., Department of Surgery, UCLA Medical Center, in the postoperative critically ill patient. While studying postoperative, high-risk, critically ill survivors and non-survivors, Shoemaker found that, in general, the survivors' cardiovascular systems maintained mean arterial pressure at a normotensive level while increasing their global blood flow to a cardiac index of greater than 4.5 liters/min/m.sup.2 and maintaining it at that level throughout the postoperative period.
In contrast, the non-survivors did not experience increased global blood low during the postoperative period. The non-survivors generally were normotensive and maintained blood flow at a cardiac index of 3.5 liters/min/m.sup.2 which is considered normal for healthy adults.
The surgical wound requires significantly increased perfusion to facilitate healing and the removal of fluids. Thus, in order to maintain adequate perfusion of all organs, the global blood flow must increase. If this condition is not met, the brain will reduce flow to selected organs in order to maintain increased perfusion of the surgical site. The organs inadequately perfused will eventually fail. Shoemaker found that the mean time at which the deaths of non-survivors occurred was approximately 90 hours postoperatively as a result of single or multiple organ failure.
Subsequently, in a controlled study, Shoemaker proved that in patients who are not in hyperdynamic sepsis and whose cardiovascular systems cannot increase the level of global blood flow to a desired hyperdynamic level, proper immediate postoperative management through volume expansion, positive inotropic support and peripherally vasoactive therapy, resulting in a cardiac index greater than 4.5 liters/min/m.sup.2 and normotension (mean arterial blood pressure approximately equal to 92 Torr), will substantially increase their chances to survive.
The implementation of the foregoing therapeutic goal has the potential for a dramatic reduction of postoperative mortalities, estimated to be approximately 400,000 annually in the U.S. alone.